However, GCC and friends are licensed under the GPL: the code is published at http://opensource.apple.com http://opensource.apple.com; their only technical barr

However, GCC and friends are licensed under the GPL: the code is published at http://opensource.apple.com http://opensource.apple.com; their only technical barrier so far is actually making it run on another OS. That's not to say they couldn't block something like that, but with GPL code it does become significantly more difficult, if not (technically, not "this would take forever to port back to Linux") impossible.